Truck tow conveyor switching apparatus

ABSTRACT

A mechanical switching apparatus for use in an automated truck tow conveyor system has a switch plate for diverting coded trucks from a main slot in a reference surface to a spur slot intersecting the main slot. A reader head, located upstream from the switch plate and in line with a given code probe on the truck, actuates a cable operatively connected to the switch plate to move the switch plate from a position in which the spur slot is closed to an open position. Improved latch means are provided on the reader head to prevent inadvertent triggering of the reader head and inadvertent opening of the switch plate. A full spur device prevents the switch plate from diverting more than a predetermined number of trucks into the spur slot.

United States Patent Swartz [541 TRUCK Tow CONVEYOR SWITCHING APPARATUS [72] Inventor: I

[73] Assignee: FMC Corporation, San Jose, Calif. [22] Filed: May 5, 1971 [21] Appl. No.: 140,397

Karlstromm', ..104/172BT Horace M. Swartz, Doylestown, Pa.

1451 Sept. 19, 1972 Swartz- 104/88 Carney 104/88 57' ABSTRACT A mechanical switching apparatus for use in an automated truck tow conveyor system has a switch plate for diverting coded trucks from a main slot in a reference surface to a spur slot intersecting the main slot. A reader head, located upstream from the switch plate and in line with a given code probe on the truck, actuates a'cable operatively connected to the switch plate to. move the switch plate from a position in which the spur slot is closed to an open position. lmproved latch means are provided on the reader head to prevent inadvertent triggering of the reader head and inadvertent openingof the switch plate. A full spur device prevents the switch plate from diverting more than a predetermined number of trucks into the spur slot.

23 Claims, 16 Drawing Figures PATENTEDsEP I 9 1912 SHEET 3 OF 6 r0, hm N m x m fff'ffl'fffllf f I I I If fl N wm QM b am NW 1 mm on, \W N N w R M R ll. r?

PATENTED 9 337? 3,691. 959

PATENTED SEP 19 I972 SHEET 5 BF 5 TRUCK TOW CONVEYOR SWITCHING APPARATUS BACKGROUND OF THE lNVENTlON 1. Field of the lnvention The truck tow conveyor switching apparatus of .the present invention finds its use in an automated conveyor system widely used to mechanize freight handling, warehousing'and industrial operations. The conveying system is a continuous and versatile conveying medium for moving platform trucks or dollie's coded fora predestined operationover a loop or an irregular shaped path. The trucks have a vertically movable tow pin which projects through a slot in the floor surface to engage an endless power driven chain below the floor surface and to thereby propel the trucks around its path.

2. Description of the Prior Art Mechanical switching systems for in-the-floor truck tow conveyors having trucks supporting code probes for engagement with mating floor cams or reader heads, whereby properly coded trucks are shunted off a main line into a particular spur line, have been used previously. In general these systems may be divided into four classes.

1n the first class, the code cams are fixedly supported on the floor surface on which the truck moves. Typical examples of this system are shown in U. S. Pat. No. 2,936,719 issued to R. D. Rodd, U. S. Pat. No. 3,126,838 issued to L. Bradt and U. S. Pat. No. 3,265,013 issued to A. Czarnecki.

In the second class, the code cams are biased to normally protrude above the floor level to be actuated by the code probes on the truck. Typical examples-of this system are shown in U. S. Pat. No. 3,103,183 issued to Bradt et al., US. Pat. No. Re. 25,245 issued to Klamp et al., U. S. Pat. No. Re. 25,723 issued to Bradt et al., U. S. Pat. No. 3,174,439 issued to Edgar et al., U. S. Pat. No. 3,3 l6,856 issued to Edgar et al., and U. S. Pat. No. 3,338,178 issued to R. P. Jones.

in the third class, the code cams are pivoted to normally protrude above the floor level to be actuated by the code probes on the truck but may also be depressed without actuating the switching mechanism when accidentally contacted by other objects, such as a fork lift truck. Typical examples of this system are shown in U. S. Pat. No. 3,261,300 issued to G. K. Johnson, U. S. Pat. No. 3,388,674 issued to J. G. Dorrance, U. S. Pat. No. 3,406,638 issued to E. C. Braun, U. S. Pat. No. 3,481,281 issued to Johnson et al., and U. S. Pat. No. 3,538,853 issued to C. A. Dehne. In addition my copending U.S. application Ser. No. 797,485 tiled Feb. 7, 1969, now U. S. Pat. No. 3,590,742 covers a mechanical switching system of this general class.

In the fourth general class, the code cams are normally held below the floor level but are raised above SUMMARY OF THE INVENTION endless chain located'directly. beneath the main slot. The main slot is intersected along its path at selected stations by spur slots and adjacent to each intersection is a switch plate for selectively diverting properly coded trucks into the spur slots. The switch plate is operative between a normally main-line-open position and a second position in which the main-line is closed and the spur slot is open. Disposed upstream from each switch plate is a reader head which serves to actuate the associated switchplate and rotate it from its normally spur-line-closed position to a spur-line-open position, whereby an oncoming truck will be diverted into the spur slot. As the truck passes the switch plate, subsequent to entering the spur slot, the tow pin on the truck contacts a cam surface on the switch plate which functions to return the switch plate to its spur-slotclosed position.

The code reader head is a substantially hemispherically shaped trigger rotatably mounted in a pivoted frame adjacent the main slot to normally protrude above the floor. The reader head is equipped with a latch, also pivoted on the reader head frame, matingly received in a pocket in the reader head to prevent acthe floor for actuation when a truck approaches the switching area. Typical examples of this system are shown in U. S. Pat. No. 3,127,849 issued to P. Klamp, U. S. Pat. No. 3,418,944 issued to Hansford et al., U. S. Pat. No. 3,418,945 issued to Stevenson et al., U. S. Pat. No. 3,503,335 issued to L. J. Bishop, and U. S. Pat. No. 3,541,963 issued to K. R. M. Karlstrom.

cidental rotation of the reader head. The reader head further has a notch and an upper abutment surface formed in its upstream side for releasably catching a coded probe depending from the truck after the latch is released. The lower side of the reader head has a depending lug to which a push-pull cable is secured and a lower abutment surface for mating with a lower portion of the latch to prevent excessive rotation of the reader head. Thus the code probe first contacts the pivoted latch to release it and then engages the upper abutment surface of the reader head to rotate the reader head and tension the push-pull cable which rotates the switch plate.

The above latched reader head is an improvement of the reader head used in the switching apparatus of my co-pending application Ser. No. 797,485. In the latter application the motion from the rotation of the reader head is first used tounlatch the switch plate and then the continuing motion is used to rotate the switch plate. It has been found that adjustment of the push-pull cable is too critical and that improper functioning occasionally results. With the present invention no motion is transferred to the switch plate until the reader head is unlatched by a proper code probe. Then the rotation of the push-pull cable operates directly on the switch blade to rotate it. While the connection of the cable to the switch plate is through a flexible plate secured to the switch plate, this readily provides for the normal rotation of the switch plate plus also providing for some over-travel motion of the cable without damage to the parts. As a result, it is more positive in its action, is less critical in its adjustment and prevents accidental actuation of the switch plate.

The horizontal switch plate is provided with two vertical arms or narrow bars secured to the underside of the plate approximately at right angles to each other. A relatively long flexible steel plate, which is approxi mately parallel to' the spur-slotfis removably clamped at one end between the first depending bar secured to the switch plate and a second plate appreciably wider than the first depending bar. The push-pull cable is secured to this flexible plate adjacent its free end. Under the clamped mounting the flexible plate is able to bend as a spring member. The flexibility of the plate further permits over-travel motion of the cable by bending. The difference in'width of the clamping members permits a difference in the freedom of bending, or spring rate, of the flexible plate in flexing in one direction as compared to flexing in the opposite direction.-A stiff spring rate on the flexible plate is desirable to obtain quick response from the normal pulling of the cable to rotate the switch plate to the spur-slot-open position as a result of the actuation of the reader head. The bending of thefree end of the flexible plate is limited by the relatively wider width of the clamping plate as compared to the narrow bar on the opposite side of the flexible plate. A softer spring rate on the flexible plate is desirable to prevent damage to the mechanism when some outside force accidentally strikes and moves the switch plate itself to the spur-slot-open position. This causes the narrow first depending bar to push the clamped end of the flexible plate while the free end and the attached cable remain relatively stationary. Since the flexible plate-thus flexes about the narrow bar, a longer length of the flexible plate is free to bend and thus flexes with less restriction than when the cable pulls the flexible plate in the normal operation.

The switching device of this invention is also provided with a control device to indicate that the spur slot is full of trucks. The second bar secured to the switch plate, which is approximately perpendicular to the spur slot, provides a means for attaching a second push-pull following detailed Stillanotherobject is to provide a full spur control device operable in conjunction with a latchable reader head to prevent a switch from diverting a truck whenthere is no more space in the spur for another truck.

The manner in which these and other objects of the invention may be obtained will be apparent from the description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS engaged from the pusher when desired, the view being taken on line 4-4 of FIG. 3.

cable from the control device to the switch plate. This second cable passes through a slot in the second depending bar from the switch plate and a compression spring is mounted between this bar and a collar secured to the outerend of the push-pull cable. When this cable is tensioned, it rotates the switch plate to the spur-slotclosed position. If the reader head is activated by a proper code probe to divert a truck into the spur slot, the reader head cable will rotate the switch plate to the spur-slot-open position but the full spur control device will immediately cause the switch plate to return to its spur-sIot-closed position under the force of the compressed spring on the second push-pull cable. Thus the truck is prevented from entering a full spur slot and a jam-up is prevented as the truck continues along the main slot.

Accordingly, it is an object of this invention to provide an improved switching apparatus in a truck tow conveyor system.

Another object is to provide a latch directly on the code reader head that will prevent the rotatable reader head from rotating and the switch from being accidentally actuated except by a properly coded probe.

FIG. 5 is an enlarged longitudinal central section through the reader head assembly taken on line 55 of FIG. 2.

FIG. 6 is an enlarged elevational section of the reader head, showing the latch released by the code probe before rotation of the reader head- FIG. 7 is an enlarged elevational section of th reader head, showing the latch released and the code probe rotating the reader head.

FIG. 8 is an enlarged elevational section of the reader head, showing the maximum rotation of the reader head with the latch engaging the lower projection of the reader head.

FIG. 9 is an enlarged elevational section of the reader head and its pivotable support, showing the support pivoted to a slightly depressed position so the code probe is released and the reader head is in its'actuated position. 1 1

FIG. 10 is a sectional view of the pivoted reader head assembly taken'on line 10-10 of FIG. 2.

FIG. 11 is an elevationalview of the pivoted reader head assembly taken on line l111 of FIG. 2.'

FIG. 12 is an end elevational view of the pivoted reader head assembly taken on line 12-12 of FIG. 1 1.

FIG. 13 is a plan view of the pivoted reader head assembly taken on line 1313 of FIG. 11.

FIG. 14 is a fragmentary perspective view of the switch plate, showing the relative location of the respective parts.

FIG. 15 is a fragmentary perspective view of the control device that prevents entry of additional trucks when the spur is full.

FIG, 16 is a sectional view taken on line 16-16 of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The switching apparatus of the present invention, generally designated 20 in FIGS. 1 and 2, finds its primary use in a truck tow system, wherein trucks or dollies 22 are towed by a power driven chain 23 (FIG. 3) along an endless slot 24 in a reference surface such as the floor 25 of a warehouse. The main slot is intertive position. The tow pin 30 is moved to its inoperative position by raising it within sleeve 31 by means of haridle 32 so that the lower end of the tow pinis abovethe floor level. To leave the tow pin in its raised inoperative position, the handle 32 is merely rotated above the sleeve until it will not slip down into the slot 33. In the tow pin s lowered operative position, its lower end pro- The reader head 40 rotates as the truck passes coded to be diverted into the associated spur slot 26.

there'over and pulls the cable 44 which functions to rotate switch plate 42 from the inoperative, full line position of FIG. 2 to the phantom line operating position, whereby the tow pin 30 depending from the truck 22 will be diverted into the spur slot 26.

The entire reader head assembly generally designated 50 in FIG. 5 is mounted in a housing 51 having a cover plate 52 with an aperture 58 through which the reader head 40 protrudes above the floor surface 25. The cover plate 52 is secured to the housing 51 with two flat head cap screws 53 and nuts 54. The reader head 40 is a generally hemispherically shaped unit with two arms 55 depending fromthe bottom thereof to receive one end of the push-pull cable 44 and in addition the reader head is equipped with a pivoted latch member 56. The reader head 40 is rotatably mounted je'cts through the tow pin slot and releasably fits into a pocket 35 (FIGS. 3 and 4 in a pusher link 36 or the chain 23 such that when the truck 22has been diverted into a spur slot 26, by the switching apparatus 20, the tow pin will easily slide laterally along the face of pusher dog 37 and out of pocket 35 to pass freely down the spur slot 26. The pusher link 36 is attached at spaced intervals in chain 23. The chain moves directly beneath the main slot 24 to propel the trucks along.

However, when the truck 22 has been directed from the main slot 24 into the spur slot 26, the truck is no longer towed by the chain 23 because the tow pin 30 slides out of engagement with the'pusher link 36 and follows a path beneath the main slot 24. The spur slot 26 may be non-powered and the truck proceeds away from the switching area under its own momentum or by gravity under a sloping floor or it may be powered by a second chain under the spur slot.

Disposed on the truck, in alignment transversely of the truck with the tow pin 30, are a series of probes 39 which are mounted in a manner similar to'the manner in which the tow pin 30 is mounted. They are manually movable from a lower operable position, wherein the lower end of the probe is slightly elevated from the floor 25 to a raised inoperable position. In their lower operable position the probes serve to trip reader heads 40 which actuate the switching apparatus 20, as will be explained more fully later. The probes 39 are located on both sides of the tow pin and are lettered so that particular trucks can be coded by lowering a selected probe into operable position. For example, the 24 probes illustrated can be lettered A to X and probe E could be lowered to its operable position leaving probes A to D and F to X in their raised inoperable position. This particular'truck would then be coded E and could then be automatically sent to a station, such as the one generally indicated by reference numeral 27, which is also coded E by the spacing of the associated reader head 40 laterally from main line slot 24. The manner in which the truck is diverted from the main slot 24 at station 28 by the switching apparatus 20 will become clear with the detailed description below.

The switching apparatus20 basically comprises the reader head 40, a switch plate 42 and a flexible pushpull cable 44 which operatively connects the reader head and the switch plate. As best shown in FIG, 2, when a truck 22 progresses d'own main slot 24 in the direction of the arrow, it will trip reader head 40 if it is on a horizontal shaft 57 and the latch 56 is pivotally mounted on a horiaontal shaft 59, both shafts extending between two arms of a bracket 60 near one of the ends of the bracket. Bracket 60 is pivotally mounted at the other of its ends in housing 51, as will be described more fully later. A pocket 62, having an abutment surface 63 and a width slightly greater than the diameter of the probes 39, iscut in the top and forward surface of the hemispherical portion of the reader head 40. A slot 64 narrower in width than the diameter of the probes 39 is further provided in the reader head 40 deeper into pocket 62 to receive the pivoted latch 56. The lower end of probe 39 first contacts latch 56 rotating it counterclockwise to release it from its latched position and then engages abutment surface 63 rotating the reader head 40 counterclockwise, as shown in FIGS. 5 to 8, about the shaft 57. Before the probe 39 can ride off the top of abutment surface 63 of reader head 40, the reader head is depressed into the housing slightly by the pivoting of bracket 60, as shown in FIG. 9. The push-pull cable 44 is secured to a spring type hollow pin 65 which extends between the two depending arms 55 of the reader head and is pivotable therein. Therefore, as reader head 40 is rotated counterclockwise by the probe 39 moving from right to left, the two depending arms 55 of the reader head 40 are moved generally from left to right, as viewed in FIGS. 5-9, pulling cable 44 which rotates switch plate 42 from a spur-slot-clos'ed position to a spur-slot-open position as will be described later.

The pivoted bracket 60, as shown in FIGS. 5, 10-13, comprises two longitudinal side members 70, pivot pin 71, a lower stop bar 72, an upper stop bar 73, a transverse tie bar 74, a pair of upper resilient bumpers 75 and a pair of upper spring guides 76. Transverse bar 74 ties the two outer ends of side members together and pivot pin 71 secured in the pivot end of these side members completes the rectangular frame work forming this pivoted bracket. Bumpers consist of a rectangular piece of sponge rubber or soft rubber strip cemented to the top of member 74 to act as a resilient cushioning member in the seating of the free end of the pivoted bracket against the underside of the cover plate 42. Adjacent to transverse bar 74 a hole is provided in each side member 70 to receive the horizontal shaft 59 for the pivoted latch 56 and a hole located in alignment with the center of reader head 40 is provided in each side member 70 to the reader head-Between the reader head pivot shaft 57 and the latch pivot shaft 59, there is a bar 73 welded to each side member 70 near their top edge which forms an upper stop for the pivoted latch 56. Adjacent to the reader head 40 there is a bar 72 welded to each side member 70 near their bottom edge which forms a stop for the rearward end of the two depending arms 55 of the reader head. Stop member 72 retains the reader head 40 from exceeding its normal upright position and stop member 73 retains the latch 56 from rising above the outer circumferential surface of the hemispherical portion of reader head 40. The pivotpin 71 of bracket 60 is supported in a sleeve 77 welded to a horizontal plate 78 which is removably secured to a transverse support plate 79 welded to the sides of housing 51. Bolts 80, nuts 81, washers 82 and spacer plate 83 are used tofasten plate 78 to transverse support plate 79. Between the reader head'pivot shaft 57 and the upper stop bar 73 a spring guide 76 is welded to the outer side of each side member 70, as shown in FIGS. and 11. Vertically below the spring guides 76 a lower pair of spring guides 84 are welded to the'bottom of housing 5l. A spring 61 is mounted between the upper guides 76 and the lower guide 84 on each side of side members 70 to resiliently support the pivoted bracket 60.

To prevent an inadvertent tripping of a reader head,

and thereby an incorrect switch plate movement, by

means other than aprobe 39, the pivoted latch 56 is provided within the reader head 40 itself, as shown in FIGS. 5, 11-13. The latch 56 comprises a rearwardly facing curved central member 90 having a forward extension 91 for the pivot shaft 59. A sleeve 92 extends transversely from each side of extension 91 and mounts over shaft 59 to provide pivotal movement of latch 56. A transverse arcuate shaped. plate 93 is provided in the top surface of the curved central member 90 to provide greater width than the thickness of the central member 90 for the probe 39 to engage the latch. A square stop bar 94 is attached to the bottom of the rearwardly facing curved central member and extends transversely of the thickness of this central member 90. A cylindrical pin 95 is welded to the central plate 90 below and slightly to the rear of pivot sleeve 92. A torsional spring a 96 is wound around pivot sleeve 92 with one of its ends extending under transverse bar 74 and the other end extending under pin 95 as spring stops. The latch 56 is pivotally mounted on pivot pin 59 so that the curved central member 90 projects within slot 64 and the plate 93 and stop bar 94 project only within pocket 62 of the reader head 40. In the normal position of reader head 40, as shown in FIG. 5, the stop bar 94 prevents rotation of reader head 40 because the transverse ends of stop bar 94 extend beyond slot 64 but are within the lower end of pocket 62. When the latch 56 is released by a probe 39, as shown in FIG. 6, the latch pivots counterclockwise so that the stop bar 94 is out of and below pocket 62, thus releasing reader head 40 so it can rotate. The reader head is free to rotate until stop bar 94 contacts the forward end of the two depending arms 55 of the reader head, as shown in FIG. 8. As the code probe continues its forward motion, the bracket 60 on which the reader is mounted pivots, as shown in FIG. 9.

The switch plate 42 (FIG. 2) is rotatably mounted adjacent the intersection of the main slot 24 and the associated spur slot 26 on a vertical tubular column 100 so that it can rotate between an open and a closed position. In its spur-slot-open position, shown by phantom lines in FIG. 2, the switch plate 42 presents an abutment surface across the main slot 24 to divert the tow pin 30 of a truck 22 traveling along the main slot 24 into the adjacent spur slot 26. Formed on a rearward portion of the switch plate 42 is a cam surface 101 which presents an abutment surface across the spur slot when the switch plate is in its open position. The tow pin 30 of a truck that has been diverted into the shunt slot will engage the cam surface 101 and thereby rotate the switch plate to its spur-sIot-closed position, shown by solid lines in FIG. 2, so that other trucks will not be diverted by the switch plate 42 unless they actuate the associated reader head 40. v

Push-pull cable 44 is operably connected from reader head assembly 50 to the switch plate 42, as shown in FIGS. 2 and 14. The push-pull cable 44 consists of an inner core 45 and an outer casing 46. As shown in FIG. 5, the end of the casing near the reader head is clamped in an upright slotted support member 47 secured to the housing 51 and only the inner movable core is connected to the reader head 40. Since the push-pull cable 44 is usually buried and inaccessible in the distance between reader head housing 51 and a switch plate housing 102, the cable is usually placed in a protective flexible hose 48 between these housings so that the push-pull cable may be removed if necessary. The hose is clamped to a short metal tube 103 welded over the cable opening in each housing with hose clamps 104. In the switch plate housing 102, as shown in FIG. 14, the end of the push-pull cable casing 46 is clamped in another upright slotted support member 105 secured to the housing 102. The movable inner core 45 extends beyond this member to the switch plate 42. A vertical bar 106 depends from the underside of the switch plate 42 adjacent to the vertical tubular column 100 and is secured to the switch plate. A flexible spring plate 107 is clamped between bar 106 and a plate 108 with bolts 109 and nuts 110. The outer vertical edge of bar 106 and plate 108 adjacent to spring plate 107 is rounded to permit the spring plate to flex without creating a stress raiser at the point of bending. The spring plate 107 extends radially out from pivot column 100 approximately parallel to the spur slot 26 and on the opposite side of column 100 from the main line slot 24. Near the outer end of spring plate 107 and in alignment with the push-pull cable 44 a slotted hole 111 is provided. The threaded end of inner core 45 of push-pull cable 44 is inserted through the slotted hole 1 l1 and secured to the spring plate 107 with a locknut 112 on each side. Clamp plate 108 is wider than bar 106 so that the free length, and thereby the spring force of spring plate 107, is different when bending to one side from the other. Spring plate 107 is made flexible so that it permits some over-travel of the push-pull cable 45 after the switch plate 42 is seated in its floor plate openings at either its open or closed position. When the reader head cable 44 is actuated to open switch plate 42, it pulls against the shorter and stifi'er end of spring plate 107 so the switch plate moves more quickly and with less flexing. Likewise, when the tow pin 30 is in the spur slot 26 and engagescam surface101 on the rear of the switch plate while the switch plate is in the spur slot-open position, the switch plate will return to the spur-slot-cl'osed position more quickly because the wider clamp plate 108 is pushing spring plate 107. The latter will then return to its original position with less flexing. and pull the push-pull cable 45 with it. ln the case of an accidental movement of switch plate 42 from its spur-slot-closed position to its open position by some outsideforce, as by some projection on a fork lift truck catching in the switch plate, and with no corresponding movement of the reader head cable 45, the longer free end of spring plate 107 will permit it to flex easily in this direction without damage since plate 107 bends about narrow bar 106. Then the spring plate 107 returns the switch plate to its original position after the removal of the outside force.

ln operation when a proper probe 39 on the truck ac- I tuates the correspondingly positioned reader head 40,

the rotation of the reader head will pull the push-pull cable from left to right, as shown in FIG. 14. This movement will pull spring leaf 107 and cause the switch plate 42 to pivot from its spur-closed position to its spur-open position, as shown in phantom lines in FIG. 2. The tow pin 30 and truck 22 are then diverted into spur slot 26.

A control device, generally designated 115 in FIGS. 2 and and hereinafter referred to as full-spur device, is provided to prevent more than a predetermined number of trucks 22 from entering a spur slot. This is necessary to prevent a jam-up of the truck tow system whereby too many trucks are diverted into one spur slot 26, causing at least one truck to block main slot 24. The full-spur device 115 is pivotally mounted below the floor 25 at a point far enough along the spur slot 26 that a truck with its tow pin 30 engaging the device will not block other trucks moving in the main slot 24. The fullspur device 115 is a three bar parallel linkage cam which includes bar 116, projecting into the spur slot 26, and parallel links 117 and 118 which connect the bar 116 to a housing 119 in which the device is mounted. The links 117 and 118 are pivotally connected to the casing 119 as well as to the bar 116 by brackets 120 and pins 121 forming a parallelogram linkage, so that as the tow pin 30 of a truck 22 contacts the bar 116 it will swing out of the way of the tow pin with the links 117 and 118 swinging clockwise from their normal position, as shown in FIG. 15. A stop 122, projecting form one end of link 117, prevents the parallel linkage cam from rotating counterclockwise from its normal position by abutting against one side wall of housing 119. To retain the cam in its normal position, except when a tow pin 30 occupies the spur slot 26 adjacent the cam, a torsion spring 123 is provided to bias the link 118 in a counterclockwise direction, forcing stop 122 against casing 119. A second push-pull cable 125 operably connects the full-spur device 115 to the switch plate 42. One end of a movable inner core 116 of the push-pull cable 115 is secured to link 118 of the full-spur device and the other end supports a coil compression spring 130, as shown in FIG. 14. An outer casing 127 for the push-pull cable 125 is clamped at each of its ends to the switch plate housing 102 and the fullspur device housing 119. The spring 130 abuts a collar 132 fastened at one end of the inner core 126 of pushpull cable and has itsother end abutting a bar 131 depending from switch plate 42: Bar 131 issecured to the switch plate and has an aperture therein through which core 126 of the push-pull cable passes.

It can be seen that, when the full-spur device 115 is contacted by a tow pin 30 of a truck 22, the bar 116, which is approximately as long as a truck, is forced toward the housing119 out of the shunt slot 26, causing links 117 and 118 to rotate in a clockwise direction to pull the inner core 126 of cable 125. When the inner core 126 is pulled, spring is compressed and it biases switch plate 42 in a clockwise direction, thereby tending to maintain the switch plate in a spur-slotclosed position so that no further trucks will be diverted into the spur slot. lf, while spring 130 is compressed, another properly coded truck 22 in main slot 24 trips the reader head 40 to activate the switch plate, the switch plate will actually open but due to the added resistance of spring 130 as bar 131 rotates counter clockwise, it will immediately close again as the probe 39 releases the reader and before the truck reaches the switch plate. That truck will then remain in the main slot 24 until the full-spur device 115 is deactivated by the withdrawal of a truck in the spur slot and the compression in spring 130 is released. It should be stated that main slot 24 is continuous so that a truck 22 that was prevented from entering its predestined spur slot 26 will eventually come by the spur slot again at which time it could be diverted into the spur slot if the spur slot is no longer full. 7

Althoughthe best mode contemplated for carrying out the present invention has been shown and described herein, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What is claimed is:

l. A switching apparatus for use in a truck tow conveyor system having a continuous main slot in a reference surface for guiding a truck, said switching apparatus having at least one spur slot in said surface intersecting said main slot for accepting trucks diverted from said main slot, said trucks having at least one code probe, said switching apparatus comprising in combination:

a. a switch plate adjacent the intersection of said main slot and one of said spur slots, said switch plate being movable between a spur-slot-closed and a spur-slot-open position for physically diverting trucks in said main slot into the adjacent spur slot;

b. a reader head upstream of said switch plate adjacent said main slot projecting above said surface and responsive to the horizontal movement of a properly coded probe on the truck thereover to rotate said reader head, said reader head having an abutment surface formed in a pocket in its upwardly projecting surface to receive said code probe;

c. connecting means between said reader head and said switch plate whereby rotation of said reader head by a code probe will actuate said switch from a spur-slot-closed to a spur-slot-open position; and

d. latching means cooperatively mounted with said reader head to prevent accidental rotation of said paratus having at least one spur slot in said surface intersecting said main slot for accepting trucks diverted from said main slot, said trucks having at least one code probe, said switching apparatus comprising in combination:

a. a switch plate adjacent the intersection of said main slot and one of said spur slots, said switch plate being movable between a spur-slot-closed and a spur-slot-open position for physically diverting trucks in said main slot into the adjacent spur slot; t v a reader head upstream of said switch plate adjacent said main slot projecting above said surface and responsive to the horizontal movement of a properly coded probe on the truck thereover to rotate said reader head, said reader head having an abutment surface formed in a pocket in its upwardly projecting surface to receive said code probe;

c. connecting means between said reader head and said switch plate whereby rotation of said reader head by a code probe will actuate said switch from a spur-slot-closed to a spur-slot-open position; and

. a latch member pivotal with respect to the reader head, said latch member normally oriented to block rotation of said reader head, said latch member positioned in the path of the code probe for engagement thereby to release the reader head for rotation.

3. The switching apparatus of claim 2, wherein said latch member comprises a pivoted arm portion normally projecting above said reference surface for engagement by the code probe and a stop bar engageable with the lower surface of the pocket in said reader head to prevent accidental rotation of said reader head.

4. The switching apparatus of claim 3, wherein said reader head further has a narrow centrally located vertical slot extending forwardly and more deeply into the reader head than the pocket, wherein said reader head is rotatably mounted in a pivoted support frame and wherein said latch member further comprises a relatively thin arcuate shaped forward arm portion matingly receivable in the central slot upon engagement with and pivoting under the horizontal'movement of the code probe, said latch member having a rear portion including a horizontal sleeve and a horizontal pivot shaft within said sleeve secured in the outer end of said pivoted support frame, bias means on said sleeve for normally urging said forward arm portion to its upper operative position and a stop bar on said pivoted support frame to limit the upward travel of said forward portion of said latch member so as not to protrude above the outer surface of said reader head.

5. The switching apparatus of claim 4, wherein said pivoted support frame has a lower transverse bar and wherein said reader head further has at least one lug projecting below the lower outer surface, said lug having fastening means for one end of said connecting means, one end of said lug having an abutment surface for engaging said lower transverse bar on said pivoted support frame to limit the rotation of said reader head, the other end of said lug having an abutment surface for engaging the stop bar of said latch member to limit rotation of said reader head in the opposite direction when said latch member is released by the code probe.

6. The switching apparatus of claim 1, wherein-said switch plate further comprises a flexible plate attached to said switch plate to' provide over-travel motion between said connecting means and said switch plate, said connecting means being fastened adjacent to the outer end of said flexible plate.

7. The switching apparatus of claim 6, wherein a narrow bar is attached to the underside of said switch plate and a wider clamping plate is fastened to said narrow bar, said flexible plate is clamped between said bar and plate, the free end of said flexible plate extending appreciably beyond said wider plate to provide a different spring rate in flexing in one direction from the spring rate in flexing in the opposite direction whereby the flexible plate is stiffer when the free end of the flexible plate is normally pulled by said connecting means about the wider clamping plate to rotate said switch plate from its spur-slot-closed to its spur-slot-open position and the flexible plate is less stiff when the clamped end of the flexible plate is pushed by the narrow bar as said switch plate is rotated to the spur-slot-open position by some outside force while the free end of the flexible plate and said connecting means remains relatively stationary.

8. The switching apparatus of claim 1', wherein the switch plate further comprises a cam surface thereon for returning said switch plate to the spur-slot-closed position when contacted by the truck in the spur slot, said cam surface projecting into the spur slot when the switch plate is in the spur-slot-open position.

9. The switching apparatus of claim 1, wherein the combination further comprises a full-spur control means operatively associated with the switch plate for preventing more than a predetermined number of trucks from being diverted into said spur slot.

10. The switching apparatus of claim 9, wherein the full-spur control means comprises truck detecting means in the spur slot downstream of the switch plate, a second connecting means operatively attached at one end to said detecting means, spring means attached to the other end of said second connecting means, and an arm attached to the underside of said switch plate with which the spring means is operatively related to return said switch plate to a spur-slot-closed position when the second connecting means is actuated by the full-spur control means.

11. In combination with a switching apparatus for a truck tow conveyor having a main slot and at least one spur slot in a reference surface, the trucks having at least one code probe, a switch plate adjacent the intersection of said main slot and said spur slot operative between a spur-slot-closed and a spur-slot-open position, a pivotally supported rotatable reader head for operation by the code probe upstream of said switch plate adjacent said main slot, and means operatively connecting said switch plate and said reader head, the improvement which comprises over-travel means cooperatively associated with said switch plate and said connecting means to permit motion of said connecting means greater than the motion required to rotate said switch plate from its spur-slot-closed to its spur-slotopenvpositio'n.

12. The switching apparatus of claim 11, wherein said over-travel means comprises a spring plate operatively connected to said switch plate having a different spring rate in flexing in one direction from the spring rate in flexing in the opposite direction and wherein said connecting means is fastened to said spring plate adjacent its free end.

13. The switching apparatus of claim 12, wherein said over-travel means further comprises a relatively narrow bar attached to the underside of said switch plate and a relatively wider plate which clamps said spring plate'therebetween to the narrower bar with the free end of said spring plate extending appreciably beyond the width of the wider clamping plate whereby the spring plate is stiffer when the free end of the spring plate is normally moved against the wider clamping plate to rotate the switch plate from its spur-slot-closed to its spur-slot-open position in response to the motion of said connecting means and the spring plate is less stiff when the clamped end of the spring plate is moved by the narrow bar in the direction to open the spur slot by some outside force accidentally catching and moving the switch plate directly without motion by said connecting means.

14. In combination with a switching apparatus for a truck tow conveyor having a code probe on the truck and having a main slot and at least one spur slot in a reference surface, a switch plate adjacent the intersection of said main slot and said spur slot operative between a spur-slot-closed and a spur-slot-open position, a pivotally supported rotatable reader head for the code probe upstream of said switch plate adjacent said main slot, and means operatively connecting said switch plate and said reader head, the improvement which comprises latching means mounted adjacent said reader head and having at least one portion to engage the reader head to lock the reader head against rotation, said latching means having a surface for engagement by the code probe to release the latching means from locking engagement with said reader head so the code probe can rotate said reader head and actuate said switch plate.

15. The switching apparatus of claim 14, wherein the reader head has a pocket formed in its upwardly projecting surface and a narrow centrally located slot extending deeper into the body than said pocket, the reader head being rotatably mounted in a pivoted support frame, and wherein said latching means comprises a relatively thin arcuate shaped forward arm matingly received in said central slot of the reader head body, a rear portion including a pivot shaft for pivotally mounting said latch means in the pivoted support frame, and a lower portion having a transverse bar extending from each side overlapping said central slot and engaging the lower end of the pocket in said body in its normal operative position.

16. The switching apparatus of claim 15, wherein said latching means further comprises bias means located between said pivoted frame and said forward arm to normally keep the forward arm in an elevated position so as to be engageable with the code probe 14 prior'to the code probes engagement in the reader head's pocket and stop meanson the pivoted support frame to limit the-upward travel of the forward arm so it does not protrude above the outer surface of said reader headbody.

17. In combination with a switching apparatus for a truck tow conveyor system having a main slot and at least one intersecting spur slot in a reference surface, the trucks having at least one code probe, a switch plate adjacent the intersection of said main slot and said spur slot operative between a spur-slot-closed and a spur-slot-open position, a pivotally supported rotatable reader head for operation by the code probe upstream of said switch plate adjacent said main slot, and means operatively connecting said reader head and said switch plate, the improvement which comprises:

a. over-travel means cooperatively associated with said switch plate and said connecting means to permit motion of said connecting means greater than the motion required to rotate said switch plate from its spur-slot-closed to its spur-slot-open position and the reverse rotation of the switch plate from spur-slot-open to the spur-slot-closed position; and a latch movably mounted upstream of said reader head and having at leastone portion matingly received within said reader head, said latch normally urged into locking engagement with said reader head to prevent the rotation of said reader head, said latch having a surface engageable by an approaching code probe for releasing said reader head: from the locked position prior to the probes engagement with said reader head.

18. A reader head for use in a truck tow conveyor system having a reference surface on which the truck moves and switching means for diverting a truck with a code probe from a main line slot to a preselected intersecting spur slot in the reference surface, the combination which comprises:

a. a rotatable reader head body responsive to the horizontal movement of a properly coded truck thereover, said reader head in its normal operative position having a pocket formed in its upwardly projecting surface with a vertical abutment surface for disengagingly receiving said code probe;

b. a pivoted frame for rotatably supporting said reader head body, said frame being resiliently supported to normally bias said reader head to project above the reference surface and to depress below the reference surface without rotating said body under the action of any other force than a properly located code probe; and I c. latching means pivotally mounted adjacent said reader head and adjacent the outer end of said pivoted frame to normally lock said reader head from rotating, said latching means having a portion nested within the pocket in said reader head for engagement by the code probe to release said reader head whereby said reader head body is prevented from rotating by the horizontal movement of the code probe until the latching means is first released by the code probe.

19. The reader head of claim 18, wherein the reader head body further comprises a narrow centrally located vertical slot extending deeper into the body than the 20. The reader head of claim 19, wherein the latching means comprises a narrow arcuate shaped rearward portion matingly received in said narrow centrally located slot in the reader head body, a forward portion including a horizontal sleeve and a horizontal shaft within the sleeve for pivotally mounting said latching means in said pivoted frame, bias means on said latching means for normal urging said latching means to its upper position within the outline of the upper surface of said reader head body and a stop bar secured to a lower portion of said latching means extending transversely of each side of said narrow rearward portion so as to engage the lower surface of the pocket to lock said reader head against rotation.

21. The reader head of claim 19, wherein said pivoted frame has a lower transverse bar located rearward of the rotatable axis of said reader head body to engage one end of the lug projecting below said body to limit the rotation of said body in one direction, an upper transverse bar located rearward of the pivot for the latch means to limit the upward movement of the latching means and resilient means on the outer end of the pivoted frame to limit the upward movement of the pivoted frame.

22. The reader head of claim 21, wherein said reader head body further has an abutment surface on the end of the lower lug adjacent to the pivot for the latching means for engaging the stop bar on the latching means after the latching means has released the reader head to limit rotation of said reader head in a direction opposite to that limited by said'lower transverse bar.

23. The reader head of claim 22, wherein the reader head further comprises flexible connecting means attached to the lower lug on the reader head body and to the switching means on its other end for actuating the switch plate in response to rotation of the unlatched reader head body. 

1. A switching apparatus for use in a truck tow conveyor system having a continuous main slot in a reference surface for guiding a truck, said switching apparatus having at least one spur slot in said surface intersecting said main slot for accepting trucks diverted from said main slot, said trucks having at least one code probe, said switching apparatus comprising in combination: a. a switch plate adjacent the intersection of said main slot and one of said spur slots, said switch plate being movable between a spur-slot-closed and a spur-slot-open position for physically diverting trucks in said main slot into the adjacent spur slot; b. a reader head upstream of said switch plate adjacent said main slot projecting above said surface and responsive to the horizontal movement of a properly coded probe on the truck thereover to rotate said reader head, said reader head having an abutment surface formed in a pocket in its upwardly projecting surface to receive said code probe; c. connecting means between said reader head and said switch plate whereby rotation of said reader head by a code probe will actuate said switch from a spur-slot-closed to a spur-slot-open position; and d. latching means cooperatively mounted with said reader head to prevent accidental rotation of said reader head and to contact the code probe prior to its engagement with the abutment surface of said reader head whereby such engagement will release said reader head for rotation by the code probe.
 2. A switching apparatus for use in a truck tow conveyor system having a continuous main slot in a reference surface for guiding a truck, said switching apparatus having at least one spur slot in said surface intersecting said main slot for accepting trucks diverted from said main slot, said trucks having at least one code probe, said switching apparatus comprising in combination: a. a switch plate adjacent the intersection of said main slot and one of said spur slots, said switch plate being movable between a spur-slot-closed and a spur-slot-open position for physically diverting trucks in said main slot into the adjacent spur slot; b. a rEader head upstream of said switch plate adjacent said main slot projecting above said surface and responsive to the horizontal movement of a properly coded probe on the truck thereover to rotate said reader head, said reader head having an abutment surface formed in a pocket in its upwardly projecting surface to receive said code probe; c. connecting means between said reader head and said switch plate whereby rotation of said reader head by a code probe will actuate said switch from a spur-slot-closed to a spur-slot-open position; and d. a latch member pivotal with respect to the reader head, said latch member normally oriented to block rotation of said reader head, said latch member positioned in the path of the code probe for engagement thereby to release the reader head for rotation.
 3. The switching apparatus of claim 2, wherein said latch member comprises a pivoted arm portion normally projecting above said reference surface for engagement by the code probe and a stop bar engageable with the lower surface of the pocket in said reader head to prevent accidental rotation of said reader head.
 4. The switching apparatus of claim 3, wherein said reader head further has a narrow centrally located vertical slot extending forwardly and more deeply into the reader head than the pocket, wherein said reader head is rotatably mounted in a pivoted support frame and wherein said latch member further comprises a relatively thin arcuate shaped forward arm portion matingly receivable in the central slot upon engagement with and pivoting under the horizontal movement of the code probe, said latch member having a rear portion including a horizontal sleeve and a horizontal pivot shaft within said sleeve secured in the outer end of said pivoted support frame, bias means on said sleeve for normally urging said forward arm portion to its upper operative position and a stop bar on said pivoted support frame to limit the upward travel of said forward portion of said latch member so as not to protrude above the outer surface of said reader head.
 5. The switching apparatus of claim 4, wherein said pivoted support frame has a lower transverse bar and wherein said reader head further has at least one lug projecting below the lower outer surface, said lug having fastening means for one end of said connecting means, one end of said lug having an abutment surface for engaging said lower transverse bar on said pivoted support frame to limit the rotation of said reader head, the other end of said lug having an abutment surface for engaging the stop bar of said latch member to limit rotation of said reader head in the opposite direction when said latch member is released by the code probe.
 6. The switching apparatus of claim 1, wherein said switch plate further comprises a flexible plate attached to said switch plate to provide over-travel motion between said connecting means and said switch plate, said connecting means being fastened adjacent to the outer end of said flexible plate.
 7. The switching apparatus of claim 6, wherein a narrow bar is attached to the underside of said switch plate and a wider clamping plate is fastened to said narrow bar, said flexible plate is clamped between said bar and plate, the free end of said flexible plate extending appreciably beyond said wider plate to provide a different spring rate in flexing in one direction from the spring rate in flexing in the opposite direction whereby the flexible plate is stiffer when the free end of the flexible plate is normally pulled by said connecting means about the wider clamping plate to rotate said switch plate from its spur-slot-closed to its spur-slot-open position and the flexible plate is less stiff when the clamped end of the flexible plate is pushed by the narrow bar as said switch plate is rotated to the spur-slot-open position by some outside force while the free end of the flexible plate and said connecting means remains relatively stationary.
 8. The switching apparatus of claim 1, wherein the switch plate further comprises a cam surface thereon for returning said switch plate to the spur-slot-closed position when contacted by the truck in the spur slot, said cam surface projecting into the spur slot when the switch plate is in the spur-slot-open position.
 9. The switching apparatus of claim 1, wherein the combination further comprises a full-spur control means operatively associated with the switch plate for preventing more than a predetermined number of trucks from being diverted into said spur slot.
 10. The switching apparatus of claim 9, wherein the full-spur control means comprises truck detecting means in the spur slot downstream of the switch plate, a second connecting means operatively attached at one end to said detecting means, spring means attached to the other end of said second connecting means, and an arm attached to the underside of said switch plate with which the spring means is operatively related to return said switch plate to a spur-slot-closed position when the second connecting means is actuated by the full-spur control means.
 11. In combination with a switching apparatus for a truck tow conveyor having a main slot and at least one spur slot in a reference surface, the trucks having at least one code probe, a switch plate adjacent the intersection of said main slot and said spur slot operative between a spur-slot-closed and a spur-slot-open position, a pivotally supported rotatable reader head for operation by the code probe upstream of said switch plate adjacent said main slot, and means operatively connecting said switch plate and said reader head, the improvement which comprises over-travel means cooperatively associated with said switch plate and said connecting means to permit motion of said connecting means greater than the motion required to rotate said switch plate from its spur-slot-closed to its spur-slot-open position.
 12. The switching apparatus of claim 11, wherein said over-travel means comprises a spring plate operatively connected to said switch plate having a different spring rate in flexing in one direction from the spring rate in flexing in the opposite direction and wherein said connecting means is fastened to said spring plate adjacent its free end.
 13. The switching apparatus of claim 12, wherein said over-travel means further comprises a relatively narrow bar attached to the underside of said switch plate and a relatively wider plate which clamps said spring plate therebetween to the narrower bar with the free end of said spring plate extending appreciably beyond the width of the wider clamping plate whereby the spring plate is stiffer when the free end of the spring plate is normally moved against the wider clamping plate to rotate the switch plate from its spur-slot-closed to its spur-slot-open position in response to the motion of said connecting means and the spring plate is less stiff when the clamped end of the spring plate is moved by the narrow bar in the direction to open the spur slot by some outside force accidentally catching and moving the switch plate directly without motion by said connecting means.
 14. In combination with a switching apparatus for a truck tow conveyor having a code probe on the truck and having a main slot and at least one spur slot in a reference surface, a switch plate adjacent the intersection of said main slot and said spur slot operative between a spur-slot-closed and a spur-slot-open position, a pivotally supported rotatable reader head for the code probe upstream of said switch plate adjacent said main slot, and means operatively connecting said switch plate and said reader head, the improvement which comprises latching means mounted adjacent said reader head and having at least one portion to engage the reader head to lock the reader head against rotation, said latching means having a surface for engagement by the code probe to release the latching means from locking engagement with said reader head so the code probe can rotate said reader head and actuate said switch plate.
 15. The switching apparatus of claim 14, wherein the reader head has a pocket formed in its upwardly projecting surface and a narrow centrally located slot extending deeper into the body than said pocket, the reader head being rotatably mounted in a pivoted support frame, and wherein said latching means comprises a relatively thin arcuate shaped forward arm matingly received in said central slot of the reader head body, a rear portion including a pivot shaft for pivotally mounting said latch means in the pivoted support frame, and a lower portion having a transverse bar extending from each side overlapping said central slot and engaging the lower end of the pocket in said body in its normal operative position.
 16. The switching apparatus of claim 15, wherein said latching means further comprises bias means located between said pivoted frame and said forward arm to normally keep the forward arm in an elevated position so as to be engageable with the code probe prior to the code probe''s engagement in the reader head''s pocket and stop means on the pivoted support frame to limit the upward travel of the forward arm so it does not protrude above the outer surface of said reader head body.
 17. In combination with a switching apparatus for a truck tow conveyor system having a main slot and at least one intersecting spur slot in a reference surface, the trucks having at least one code probe, a switch plate adjacent the intersection of said main slot and said spur slot operative between a spur-slot-closed and a spur-slot-open position, a pivotally supported rotatable reader head for operation by the code probe upstream of said switch plate adjacent said main slot, and means operatively connecting said reader head and said switch plate, the improvement which comprises: a. over-travel means cooperatively associated with said switch plate and said connecting means to permit motion of said connecting means greater than the motion required to rotate said switch plate from its spur-slot-closed to its spur-slot-open position and the reverse rotation of the switch plate from spur-slot-open to the spur-slot-closed position; and b. a latch movably mounted upstream of said reader head and having at least one portion matingly received within said reader head, said latch normally urged into locking engagement with said reader head to prevent the rotation of said reader head, said latch having a surface engageable by an approaching code probe for releasing said reader head from the locked position prior to the probe''s engagement with said reader head.
 18. A reader head for use in a truck tow conveyor system having a reference surface on which the truck moves and switching means for diverting a truck with a code probe from a main line slot to a preselected intersecting spur slot in the reference surface, the combination which comprises: a. a rotatable reader head body responsive to the horizontal movement of a properly coded truck thereover, said reader head in its normal operative position having a pocket formed in its upwardly projecting surface with a vertical abutment surface for disengagingly receiving said code probe; b. a pivoted frame for rotatably supporting said reader head body, said frame being resiliently supported to normally bias said reader head to project above the reference surface and to depress below the reference surface without rotating said body under the action of any other force than a properly located code probe; and c. latching means pivotally mounted adjacent said reader head and adjacent the outer end of said pivoted frame to normally lock said reader head from rotating, said latching means having a portion nested within the pocket in said reader head for engagement by the code probe to release said reader head whereby said reader head body is prevented from rotating by the horizontal movement of the code probe until the latching means is first released by the code probe.
 19. The reader head of claim 18, wherein the Reader head body further comprises a narrow centrally located vertical slot extending deeper into the body than the pocket with the abutment surface, and wherein the lower end of said pocket has a surface for engaging a lower portion of the latching means and the reader head body has at least one lug projecting below the lower surface of the body.
 20. The reader head of claim 19, wherein the latching means comprises a narrow arcuate shaped rearward portion matingly received in said narrow centrally located slot in the reader head body, a forward portion including a horizontal sleeve and a horizontal shaft within the sleeve for pivotally mounting said latching means in said pivoted frame, bias means on said latching means for normal urging said latching means to its upper position within the outline of the upper surface of said reader head body and a stop bar secured to a lower portion of said latching means extending transversely of each side of said narrow rearward portion so as to engage the lower surface of the pocket to lock said reader head against rotation.
 21. The reader head of claim 19, wherein said pivoted frame has a lower transverse bar located rearward of the rotatable axis of said reader head body to engage one end of the lug projecting below said body to limit the rotation of said body in one direction, an upper transverse bar located rearward of the pivot for the latch means to limit the upward movement of the latching means and resilient means on the outer end of the pivoted frame to limit the upward movement of the pivoted frame.
 22. The reader head of claim 21, wherein said reader head body further has an abutment surface on the end of the lower lug adjacent to the pivot for the latching means for engaging the stop bar on the latching means after the latching means has released the reader head to limit rotation of said reader head in a direction opposite to that limited by said lower transverse bar.
 23. The reader head of claim 22, wherein the reader head further comprises flexible connecting means attached to the lower lug on the reader head body and to the switching means on its other end for actuating the switch plate in response to rotation of the unlatched reader head body. 